Composite solid electrolyte and preparation method and application thereof

Abstract

The invention provides a composite solid-state electrolyte and a preparation method and application thereof, and relates to the technical field of solid-state electrolytes.The preparation method of the composite solid-state electrolyte comprises the following steps that (a) polymethyl methacrylate and lithium aluminum titanium phosphate are mixed and formed and then subjected to calcination treatment, and porous lithium aluminum titanium phosphate is obtained; (b) mixing the porous titanium lithium aluminum phosphate obtained in the step (a) with a polymer electrolyte solution, and drying to obtain a composite solid electrolyte; wherein the polymer electrolyte solution contains a polymer matrix and a lithium salt. According to the invention, the technical problems of long preparation time, low production efficiency and difficulty in remarkably improving the ionic conductivity of the solid electrolyte in the prior art are solved, and the technical effects of simple and feasible preparation process, high controllability, high ionic conductivity of the product, strong mechanical property and good cycling stability are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of solid electrolytes, and in particular to a composite solid electrolyte and a preparation method and application thereof. Background Art

[0002] At present, commercial lithium-ion batteries mainly use organic liquid electrolytes. However, organic solvents have defects such as flammability, leakage and volatility, and the battery has potential risks such as overcharging and short circuit, which makes the use of liquid organic electrolytes in lithium-ion batteries have certain safety hazards. Compared with lithium-ion batteries using liquid organic electrolytes, lithium batteries using solid electrolytes have the advantages of high safety, easy miniaturization and thin film, and are an important direction for the development of lithium batteries.

[0003] There are many types of solid electrolytes, among which polymer electrolytes have good flexibility and can adapt to the volume changes at the interface during battery charging and discharging, playing a certain role in stabilizing the interface. However, polymer electrolytes have the disadvantages of low ionic conductivity, narrow electrochemical stability window, and insufficient mechanical properties to inhibit the growth of lithium dendrites. Although many inorganic solid electrolytes have the advantages of high ionic conductivity and wide electrochemical stability window, they have the disadvantages of high brittleness, easy fracture and difficult processing. The inorganic / organic polymer composite solid electrolyte prepared by the multiphase composite method can combine the advantages of the above two materials and make up for the disadvantages. It is the solid electrolyte material with the most promising application development prospects.

[0004] However, the simple combination of polymer matrix and inorganic filler has limited effect on improving ionic conductivity. At the same time, most of the existing preparation methods of composite solid electrolyte membranes have problems such as long time consumption, low production efficiency and difficult thickness control, which are not suitable for large-scale mass production. In addition, when assembling batteries, the contact interface between the positive and negative electrodes and the electrolyte membrane often has poor contact or unstable contact, which manifests as large interface impedance, low ionic conductivity and poor electrochemical performance, which seriously limits the practical application of composite solid electrolytes.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] One of the purposes of the present invention is to provide a method for preparing a composite solid electrolyte, which is not only simple and easy to operate, but also highly controllable, and can effectively improve the ionic conductivity, mechanical properties and cycle stability of the product.

[0007] A second object of the present invention is to provide a composite solid electrolyte having the advantages of high ionic conductivity, strong mechanical properties and good cycle stability.

[0008] The third object of the present invention is to provide an application of a composite solid electrolyte, which can not only improve the safety of lithium-ion batteries, but also improve the working performance of lithium-ion batteries.

[0009] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0010] In a first aspect, a method for preparing a composite solid electrolyte comprises the following steps:

[0011] (a) mixing polymethyl methacrylate and lithium aluminum titanium phosphate and then calcining them to obtain porous lithium aluminum titanium phosphate;

[0012] (b) mixing the porous lithium aluminum titanium phosphate obtained in step (a) with a polymer electrolyte solution and then drying to obtain the composite solid electrolyte;

[0013] Wherein, the polymer electrolyte solution contains a polymer matrix and a lithium salt.

[0014] Further, in step (a), the mixing method includes mixing by ball milling;

[0015] Preferably, the rotation speed of the ball mill is 200 rpm-500 rpm;

[0016] Preferably, the ball milling time is 4 hours to 8 hours.

[0017] Furthermore, in step (a), the forming method includes pressing into tablets;

[0018] Preferably, the pressing pressure is 0.02GPa-0.2GPa;

[0019] Preferably, the pressing time is 2 minutes to 30 minutes.

[0020] Furthermore, in step (a), the calcination treatment comprises the following steps:

[0021] The first calcination treatment is first carried out at a temperature of 300°C-600°C, and then the second calcination treatment is carried out at a temperature of 700°C-1000°C.

[0022] Furthermore, the duration of the first calcination treatment is 2 hours to 5 hours;

[0023] Preferably, the second calcination treatment is performed for 6 hours to 20 hours.

[0024] Further, in step (b), the polymer matrix includes at least one of PEO, PPO, PAM, PVDF and PVDF-HFP;

[0025] Preferably, the polymer matrix is ​​PVDF-HFP.

[0026] Further, in step (b), the lithium salt includes at least one of LiTFSI, LiClO4, LiSO2CF3, LiFSI, LiPF6 and LiBF4;

[0027] Preferably, the lithium salt is LiTFSI.

[0028] Furthermore, in step (b), the mixing method includes at least one of dripping, coating, dipping and spraying;

[0029] Preferably, the solvent of the polymer electrolyte solution comprises an organic solvent;

[0030] Preferably, the organic solvent comprises at least one of N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, acetone and acetonitrile;

[0031] Preferably, the organic solvent is N,N-dimethylformamide.

[0032] In a second aspect, a composite solid electrolyte prepared by any of the preparation methods described above.

[0033] A third aspect is an application of the composite solid electrolyte described above in a lithium-ion battery.

[0034] Compared with the prior art, the present invention has at least the following beneficial effects:

[0035] The preparation method of the composite solid electrolyte provided by the present invention uses polymethyl methacrylate (PMMA) as a pore-forming agent, and forms a 3D porous aluminum titanium lithium phosphate solid electrolyte by a mixed calcination method, thereby improving the ionic conductivity; at the same time, by filling the polymer electrolyte, a porous composite solid electrolyte is obtained; the filled polymer electrolyte in the present invention serves as a fast ion transmission channel, and the 3D porous aluminum titanium lithium phosphate as a rigid skeleton not only provides excellent mechanical properties, can inhibit the growth of lithium dendrites, but also has a positive effect on the improvement of ionic conductivity. In short, the preparation method of the present invention, with the coordinated cooperation of each step, can make the solid electrolyte have a high ionic conductivity (8.79×10 -4 S cm -1 ) and better cycle stability (the capacity retention is about 83% after 250 cycles).

[0036] The composite solid electrolyte provided by the present invention has the advantages of high ion conductivity, strong mechanical properties and good cycle stability. The ion conductivity can reach 8.79×10 -4 S cm -1, the capacity retention rate after 250 cycles can reach 83%.

[0037] The application of the composite solid electrolyte provided by the present invention can not only improve the safety of lithium ion batteries, but also improve the working performance of lithium ion batteries. DETAILED DESCRIPTION

[0038] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] In the prior art, polymer gel electrolytes have poor mechanical properties and low ionic conductivity, liquid electrolytes cannot inhibit lithium dendrites, and face the problem of organic solvent volatilization and leakage, and oxide solid electrolytes have high mechanical strength, but poor contact with the positive and negative electrode interfaces and large interface resistance. In order to solve the above technical problems, the present invention is proposed.

[0040] According to a first aspect of the present invention, there is provided a method for preparing a composite solid electrolyte, comprising the following steps:

[0041] (a) mixing polymethyl methacrylate and lithium aluminum titanium phosphate and then calcining them to obtain porous lithium aluminum titanium phosphate;

[0042] (b) mixing the porous lithium aluminum titanium phosphate obtained in step (a) with a polymer electrolyte solution and then drying to obtain a composite solid electrolyte;

[0043] The polymer electrolyte solution contains a polymer matrix and a lithium salt.

[0044] The preparation method of the composite solid electrolyte provided by the present invention uses polymethyl methacrylate (PMMA) as a pore-forming agent, and forms a 3D porous aluminum titanium lithium phosphate solid electrolyte through a mixed calcination method, thereby improving the ion conductivity; at the same time, a porous composite solid electrolyte is obtained by filling with a polymer electrolyte; the filled polymer electrolyte in the present invention serves as a fast ion transmission channel, and the 3D porous aluminum titanium lithium phosphate as a rigid skeleton not only provides excellent mechanical properties, can inhibit the growth of lithium dendrites, but also has a positive effect on improving the ion conductivity.

[0045] In summary, the preparation method of the present invention, with the coordinated cooperation of various steps, can make the solid electrolyte have high ionic conductivity (8.79×10 -4 S cm -1 ) and better cycle stability (the capacity retention is about 83% after 250 cycles).

[0046] In a preferred embodiment, in step (a), the mixing method includes but is not limited to mixing by ball milling.

[0047] In the present invention, the rotation speed of the ball mill can be 200 rpm-500 rpm, and its typical but non-limiting rotation speed is, for example, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, and it can be further preferably 400 rpm, which is more conducive to the full mixing of the components; the ball milling time can be 4 hours-8 hours, and its typical but non-limiting time is, for example, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, and it can be further preferably 6 hours, which is more conducive to the full mixing of the components.

[0048] In a preferred embodiment, in step (a), the molding method includes but is not limited to pressing into tablets, and pressing into tablets is more conducive to improving the formation effect of porous lithium aluminum titanium phosphate.

[0049] In the present invention, the pressure for pressing into tablets can be 0.02GPa-0.2GPa, and its typical but non-limiting pressures are, for example, 0.02Gpa, 0.04Gpa, 0.06Gpa, 0.08Gpa, 0.1Gpa, 0.12Gpa, 0.14Gpa, 0.16Gpa, 0.18Gpa, and 0.2Gpa, and can be further preferably 0.1Gpa, which is more conducive to improving the molding effect; the pressing time can be 2 minutes-30 minutes, and its typical but non-limiting time is, for example, 2 minutes, 4 minutes, 6 minutes, 8 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, and 30 minutes, and can be further preferably 10 minutes, which is more conducive to improving the molding effect.

[0050] In a preferred embodiment, in step (a), the calcination treatment comprises the following steps:

[0051] The first calcination treatment is first carried out at a temperature of 300°C-600°C, and then the second calcination treatment is carried out at a temperature of 700°C-1000°C.

[0052] It should be noted that the present invention can remove organic matter and generate a uniform pore structure through the first calcination treatment; through the second calcination treatment, not only can the PMMA residue be completely removed, but also the formation of Li2CO3 at the grain boundary can be avoided, and the contact between the particles can be made more compact, and other impurities on the surface of the particles can be eliminated. In short, through the synergistic cooperation of the first calcination treatment and the second calcination treatment, a uniform, dense and pure target product is finally formed.

[0053] In the present invention, the temperature of the first calcination may be, for example, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, but is not limited thereto, and may be further preferably 450°C; the temperature of the second calcination may be, for example, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, but is not limited thereto, and may be further preferably 850°C.

[0054] In a preferred embodiment, the duration of the first calcination can be 2 hours to 5 hours, for example, 2 hours, 3 hours, 4 hours, and 5 hours, but is not limited thereto, and may be further preferably 4 hours; the duration of the second calcination can be 6 hours to 20 hours, for example, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, and 20 hours, but is not limited thereto, and may be further preferably 12 hours.

[0055] The temperatures and durations of the first calcination and the second calcination of the present invention can cooperate with each other, further improving the formation effect of porous lithium aluminum titanium phosphate, and further improving the ionic conductivity and mechanical properties.

[0056] In a preferred embodiment, in step (b), the polymer matrix includes but is not limited to at least one of PEO (polyethylene oxide), PPO (polyphenylene ether), PAM (polyacrylamide), PVDF (polyvinylidene fluoride) and PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), and PVDF-HFP may be further preferred.

[0057] In a preferred embodiment, in step (b), the lithium salt includes but is not limited to at least one of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiClO4 (lithium perchlorate), LiSO2CF3, LiFSI (lithium bis(fluorosulfonyl)imide), LiPF6 (lithium hexafluorophosphate) and LiBF4 (lithium tetrafluoroborate), and LiTFSI may be further preferred.

[0058] In a preferred embodiment, in step (b), the mixing method includes but is not limited to at least one of dripping, coating, dipping and spraying, and may further preferably be repeated dipping.

[0059] In the present invention, repeated impregnation is adopted for mixing, and drying treatment can be carried out after each impregnation. The total impregnation process can be 12 hours to 36 hours, for example, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 25 hours, 30 hours, 36 hours, and can be further preferably 24 hours. Repeated impregnation is more conducive to improving the filling effect of the polymer electrolyte, and thus is more conducive to improving the ionic conductivity.

[0060] In a preferred embodiment, in step (b), the solvent used in the polymer electrolyte solution includes but is not limited to an organic solvent; wherein the organic solvent includes but is not limited to at least one of N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, acetone and acetonitrile, and may further preferably be N,N-dimethylformamide.

[0061] A typical preparation method of a composite solid electrolyte comprises the following steps:

[0062] (1) polymethyl methacrylate (PMMA) and lithium aluminum titanium phosphate are fully mixed by ball milling to obtain a mixture;

[0063] Wherein, the molar ratio of lithium ions to polymethyl methacrylate in lithium aluminum titanium phosphate may be 1:(1-1.5), preferably 1:1.2;

[0064] The ball milling speed may be 200 rpm-500 rpm, preferably 400 rpm; the ball milling time may be 4 hours-8 hours, preferably 6 hours;

[0065] (2) pressing the mixed material obtained in step (1) into sheets to obtain a shaped object;

[0066] The pressing process is constant pressure pressing, the pressing pressure may be 0.02 GPa-0.2 GPa, preferably 0.1 GPa, and the pressing time may be 2 minutes-30 minutes, preferably 10 minutes;

[0067] (3) calcining the molded product obtained in step (2) twice to obtain porous lithium aluminum titanium phosphate;

[0068] The temperature of the first calcination treatment may be 300°C-600°C, preferably 450°C; the duration of the first calcination treatment may be 2 hours-5 hours, preferably 4 hours; the temperature of the second calcination treatment may be 700°C-1000°C, preferably 850°C; the duration of the second calcination treatment may be 6 hours-20 hours, preferably 12 hours;

[0069] (4) dissolving the polymer matrix and the lithium salt in an organic solvent to obtain a polymer electrolyte solution;

[0070] During the dissolution process, magnetic stirring can be used for assistance, the stirring speed can be 500 rpm-2000 rpm, preferably 800 rpm, and the stirring time can be 12 hours-24 hours, preferably 24 hours;

[0071] Wherein, the polymer matrix may be at least one of PEO, PPO, PAM, PVDF and PVDF-HFP, preferably PVDF-HFP; the lithium salt may be at least one of LiTFSI, LiClO4, LiSO2CF3, LiFSI, LiPF6 and LiBF4, preferably LiTFSI;

[0072] The organic solvent may be at least one of N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, acetone and acetonitrile, and may preferably be N,N-dimethylformamide (DMF);

[0073] (5) adding the polymer electrolyte solution obtained in step (4) to the porous lithium aluminum titanium phosphate obtained in step (3), mixing them thoroughly, and then drying them to obtain a composite solid electrolyte;

[0074] The method of adding the polymer electrolyte solution for mixing includes but is not limited to at least one of dripping, coating, dipping and spraying, and preferably repeated dipping, and drying treatment is performed after each dipping, and the total dipping process duration can be 12 hours to 36 hours, preferably 24 hours;

[0075] The drying is carried out in a vacuum oven at 60° C. for 12 to 24 hours, preferably 24 hours.

[0076] In summary, the preparation method of the composite solid electrolyte of the present invention is not only simple and easy to operate, but also highly controllable. Moreover, under the coordinated cooperation of each step and its process parameters, the solid electrolyte can have a high ionic conductivity (8.79×10 - 4 S cm -1 ) and better cycle stability (the capacity retention rate is about 83% after 250 cycles), as well as good mechanical properties.

[0077] According to a second aspect of the present invention, there is provided a composite solid electrolyte prepared by any of the preparation methods described above.

[0078] The composite solid electrolyte provided by the present invention has the advantages of high ion conductivity, strong mechanical properties and good cycle stability. The ion conductivity can reach 8.79×10 -4 S cm -1 , the capacity retention rate after 250 cycles can reach 83%.

[0079] According to a third aspect of the present invention, there is provided a use of the composite solid electrolyte described above in a lithium ion battery.

[0080] The application of the composite solid electrolyte provided by the present invention can not only improve the safety of lithium ion batteries, but also improve the working performance of lithium ion batteries.

[0081] The present invention is further described below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or directly purchased from the market.

[0082] Example 1

[0083] A method for preparing a composite solid electrolyte comprises the following steps:

[0084] (1) polymethyl methacrylate (PMMA) and lithium aluminum titanium phosphate are fully mixed by ball milling to obtain a mixture;

[0085] The molar ratio of lithium ions to polymethyl methacrylate in lithium aluminum titanium phosphate is 1:1.2;

[0086] Among them, the ball milling speed is 400 rpm, and the ball milling time is 6 hours;

[0087] (2) pressing the mixed material obtained in step (1) into sheets to obtain a shaped object;

[0088] The pressing was performed under constant pressure, the pressing pressure was 0.1 GPa, and the pressing time was 10 minutes;

[0089] (3) subjecting the molded product obtained in step (2) to a first calcination treatment at a temperature of 450° C. for 4 hours, and then to a second calcination treatment at a temperature of 850° C. for 12 hours, to obtain porous lithium aluminum titanium phosphate;

[0090] (4) dissolving the polymer matrix and the lithium salt in an organic solvent by magnetic stirring at a stirring speed of 800 rpm for 24 hours to obtain a polymer electrolyte solution;

[0091] Among them, the polymer matrix is ​​PVDF-HFP, and the lithium salt is LiTFSI;

[0092] The organic solvent used was N,N-dimethylformamide;

[0093] (5) adding the polymer electrolyte solution obtained in step (4) to the porous lithium aluminum titanium phosphate obtained in step (3), mixing them thoroughly, and then drying them to obtain a composite solid electrolyte;

[0094] The polymer electrolyte solution is added and mixed by repeated immersion, and drying is performed after each immersion. The total immersion time is 24 hours.

[0095] Drying was carried out in a vacuum oven at 60°C for 24 hours.

[0096] Example 2

[0097] This embodiment provides a method for preparing a composite solid electrolyte, which is different from Embodiment 1 only in that, in step (3), the temperature of the first calcination treatment is 300° C.;

[0098] The remaining steps and process parameters are the same as those in Example 1 to obtain a composite solid electrolyte.

[0099] Example 3

[0100] This embodiment provides a method for preparing a composite solid electrolyte, which is different from Embodiment 1 only in that, in step (3), the temperature of the first calcination treatment is 600° C.;

[0101] The remaining steps and process parameters are the same as those in Example 1 to obtain a composite solid electrolyte.

[0102] Example 4

[0103] This embodiment provides a method for preparing a composite solid electrolyte, which is different from Embodiment 1 only in that, in step (3), the temperature of the second calcination treatment is 700° C.;

[0104] The remaining steps and process parameters are the same as those in Example 1 to obtain a composite solid electrolyte.

[0105] Example 5

[0106] This embodiment provides a method for preparing a composite solid electrolyte, which is different from Embodiment 1 only in that, in step (3), the temperature of the second calcination treatment is 1000° C.;

[0107] The remaining steps and process parameters are the same as those in Example 1 to obtain a composite solid electrolyte.

[0108] Example 6

[0109] This embodiment provides a method for preparing a composite solid electrolyte, which differs from Embodiment 1 only in that, in step (3), only the first calcination treatment is performed, and the second calcination treatment is not performed;

[0110] The remaining steps and process parameters are the same as those in Example 1 to obtain a composite solid electrolyte, which has the disadvantage that it is difficult to form a pure target product (porous lithium aluminum titanium phosphate) with a uniform pore structure.

[0111] Example 7

[0112] This embodiment provides a method for preparing a composite solid electrolyte, which differs from Embodiment 1 only in that, in step (3), only the second calcination treatment is performed, and the first calcination treatment is not performed;

[0113] The remaining steps and process parameters are the same as those in Example 1 to obtain a composite solid electrolyte, which has the disadvantage that the pore structure uniformity and density of the target product (porous lithium aluminum titanium phosphate) are poor.

[0114] Example 8

[0115] This embodiment provides a method for preparing a composite solid electrolyte, which differs from Embodiment 1 only in that, in step (4), the polymer matrix is ​​PPO;

[0116] The remaining steps and process parameters are the same as those in Example 1 to obtain a composite solid electrolyte.

[0117] Example 9

[0118] This embodiment provides a method for preparing a composite solid electrolyte, which differs from Embodiment 1 only in that, in step (4), the polymer matrix is ​​PVDF;

[0119] The remaining steps and process parameters are the same as those in Example 1 to obtain a composite solid electrolyte.

[0120] Example 10

[0121] This embodiment provides a method for preparing a composite solid electrolyte, which is different from Embodiment 1 only in that in step (4), the lithium salt is LiClO4;

[0122] The remaining steps and process parameters are the same as those in Example 1 to obtain a composite solid electrolyte.

[0123] Embodiment 11

[0124] This embodiment provides a method for preparing a composite solid electrolyte, which differs from Embodiment 1 only in that, in step (4), the lithium salt is LiPF6;

[0125] The remaining steps and process parameters are the same as those in Example 1 to obtain a composite solid electrolyte.

[0126] Comparative Example 1

[0127] This comparative example provides a method for preparing a composite solid electrolyte, which is different from Example 1 only in that, in step (1), starch is used to replace polymethyl methacrylate (PMMA);

[0128] The remaining steps and process parameters are the same as those in Example 1 to obtain a composite solid electrolyte.

[0129] Compared with Example 1, the composite solid electrolyte of this comparative example has the defect that the pore-forming effect is poor, resulting in irregular pore shape of the target product (porous lithium aluminum titanium phosphate), and low strength and stability.

[0130] Comparative Example 2

[0131] This comparative example provides a method for preparing a composite solid electrolyte, which differs from Example 1 only in that, in step (1), lithium lanthanum zirconium oxide (LLZO) is used to replace lithium aluminum titanium phosphate;

[0132] The remaining steps and process parameters are the same as those in Example 1 to obtain a composite solid electrolyte.

[0133] Compared with Example 1, the composite solid electrolyte of this comparative example has the defects of low ion conductivity, high grain boundary resistance and high production cost.

[0134] Comparative Example 3

[0135] This comparative example provides a method for preparing a composite solid electrolyte, which differs from Example 1 only in that in step (2), the mixed material is not pressed into sheets, that is, the mixed material obtained in step (1) is directly calcined;

[0136] The remaining steps and process parameters are the same as those in Example 1 to obtain a composite solid electrolyte.

[0137] Compared with Example 1, the composite solid electrolyte of this comparative example has the defects of not only poor pore-forming effect but also waste of raw materials.

[0138] Comparative Example 4

[0139] This comparative example provides a method for preparing a composite solid electrolyte, which differs from Example 1 only in that, in step (4), no polymer matrix is ​​added, that is, the polymer electrolyte solution does not contain a polymer matrix;

[0140] The remaining steps and process parameters are the same as those in Example 1 to obtain a composite solid electrolyte.

[0141] Compared with Example 1, the composite solid electrolyte of this comparative example has defects in that the interface contact is poor, the impedance is large, cracks are generated, and the stability is poor.

[0142] Comparative Example 5

[0143] This comparative example provides a method for preparing a composite solid electrolyte, which differs from Example 1 only in that, in step (4), no lithium salt is added, that is, the polymer electrolyte solution does not contain lithium salt;

[0144] The remaining steps and process parameters are the same as those in Example 1 to obtain a composite solid electrolyte.

[0145] Compared with Example 1, the composite solid electrolyte of this comparative example has the defect that the ion conductivity is reduced, which is not conducive to ion transport.

[0146] Test example

[0147] The performance of the composite solid electrolytes obtained in Examples 1-11 and Comparative Examples 1-5 was tested, and the test results are shown in Table 1.

[0148] Test method:

[0149] The prepared composite solid electrolyte was used as the electrolyte, LiFePO4 as the positive electrode and lithium sheet as the negative electrode to assemble a half-cell, and the cycle stability of the half-cell was tested;

[0150] Assemble the SS / SSE / SS blocking cell to test the impedance and calculate the ionic conductivity.

[0151] Table 1

[0152]

[0153]

[0154] It can be seen from the data in Table 1 that the preparation method of the composite solid electrolyte of the present invention is not only simple and easy to operate, but also highly controllable. Moreover, under the coordinated cooperation of each step and its process parameters, the solid electrolyte can have a high ionic conductivity (8.79×10 -4 S cm -1 ) and better cycle stability (the capacity retention rate is about 83% after 250 cycles), as well as good mechanical properties.

[0155] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a composite solid electrolyte, characterized in that: The following steps are involved: (a) mixing polymethyl methacrylate and lithium aluminum titanium phosphate and then calcining them to obtain porous lithium aluminum titanium phosphate; (b) mixing the porous lithium aluminum titanium phosphate obtained in step (a) with a polymer electrolyte solution and then drying to obtain the composite solid electrolyte; Wherein, the polymer electrolyte solution contains a polymer matrix and a lithium salt.

2. The preparation method according to claim 1, characterized in that: In step (a), the mixing method includes mixing by ball milling; Preferably, the rotation speed of the ball mill is 200 rpm-500 rpm; Preferably, the ball milling time is 4 hours to 8 hours.

3. The preparation method according to claim 1, characterized in that: In step (a), the forming method includes pressing into tablets; Preferably, the pressing pressure is 0.02GPa-0.2GPa; Preferably, the pressing time is 2 minutes to 30 minutes.

4. The preparation method according to claim 1, characterized in that: In step (a), the calcination treatment comprises the following steps: The first calcination treatment is first carried out at a temperature of 300°C-600°C, and then the second calcination treatment is carried out at a temperature of 700°C-1000°C.

5. The preparation method according to claim 4, characterized in that: The duration of the first calcination treatment is 2 hours to 5 hours; Preferably, the second calcination treatment is performed for 6 hours to 20 hours.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In step (b), the polymer matrix includes at least one of PEO, PPO, PAM, PVDF and PVDF-HFP; Preferably, the polymer matrix is ​​PVDF-HFP.

7. The preparation method according to claim 6, characterized in that: In step (b), the lithium salt includes at least one of LiTFSI, LiClO4, LiSO2CF3, LiFSI, LiPF6 and LiBF4; Preferably, the lithium salt is LiTFSI.

8. The preparation method according to claim 7, characterized in that: In step (b), the mixing method includes at least one of dripping, coating, dipping and spraying; Preferably, the solvent of the polymer electrolyte solution comprises an organic solvent; Preferably, the organic solvent comprises at least one of N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, acetone and acetonitrile; Preferably, the organic solvent is N,N-dimethylformamide.

9. A composite solid electrolyte prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the composite solid electrolyte according to claim 9 in a lithium ion battery.

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